Add builtin-commands feature with init-deep command and disabled_commands config option

- New src/features/builtin-commands/ module with CommandDefinition loader
- Implements init-deep command for hierarchical AGENTS.md knowledge base generation
- Adds BuiltinCommandName and BuiltinCommandNameSchema to config
- Integrates builtin commands loader into main plugin with proper config merging
- Supports disabling specific builtin commands via disabled_commands config array

🤖 Generated with assistance of https://github.com/code-yeongyu/oh-my-opencode

src/config/index.ts

@@ -5,6 +5,7 @@ export {
   McpNameSchema,
   AgentNameSchema,
   HookNameSchema,
+  BuiltinCommandNameSchema,
   SisyphusAgentConfigSchema,
   ExperimentalConfigSchema,
 } from "./schema"
@@ -16,6 +17,7 @@ export type {
   McpName,
   AgentName,
   HookName,
+  BuiltinCommandName,
   SisyphusAgentConfig,
   ExperimentalConfig,
   DynamicContextPruningConfig,